Python & SnakeSQL - raise lock.LockError('Lock no longer valid.') ERROR - sql

Question

I am trying to run a python script (createdb.py) which has DB operations from my main python script (app.py) but having the below error.
Traceback (most recent call last):
File "C:\Python27\lib\site-packages\web\application.py", line 236, in process
return self.handle()
File "C:\Python27\lib\site-packages\web\application.py", line 227, in handle
return self._delegate(fn, self.fvars, args)
File "C:\Python27\lib\site-packages\web\application.py", line 409, in _delegate
return handle_class(cls)
File "C:\Python27\lib\site-packages\web\application.py", line 384, in handle_class
return tocall(*args)
File "D:\Python\virtualenvs\new4\textweb\bin\app.py", line 16, in GET
createdb.createTables()
File "D:\Python\virtualenvs\new4\textweb\bin\createdb.py", line 9, in createTables
cursor.execute("CREATE TABLE table (dateColumn Date, numberColumn Integer)")
File "D:\Python\virtualenvs\new4\textweb\bin\SnakeSQL\driver\base.py", line 1548, in execute
self.info = self.connection._create(parsedSQL['table'], parsedSQL['columns'], parameters)
File "D:\Python\virtualenvs\new4\textweb\bin\SnakeSQL\driver\base.py", line 993, in _create
self._insertRowInColTypes(table)
File "D:\Python\virtualenvs\new4\textweb\bin\SnakeSQL\driver\base.py", line 632, in _insertRowInColTypes
], types= ['String','String','String','Bool','Bool','Bool','Text','Text','Integer']
File "D:\Python\virtualenvs\new4\textweb\bin\SnakeSQL\driver\dbm.py", line 61, in _insertRow
self.tables[table].file[str(primaryKey)] = str(values)
File "D:\Python\virtualenvs\new4\textweb\bin\SnakeSQL\external\lockdbm.py", line 50, in __setitem__
raise lock.LockError('Lock no longer valid.')
LockError: Lock no longer valid.
Here is my createdb.py code;
import SnakeSQL
connection = SnakeSQL.connect(database='test', autoCreate=True)
connection = SnakeSQL.connect(database='test')
cursor = connection.cursor()
def createTables():
cursor.execute("CREATE TABLE table (dateColumn Date, numberColumn Integer)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2003-11-8', 3)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2004-11-8', 4)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2005-11-8', 5)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2006-11-8', 6)")
def select():
selectResult = cursor.execute("SELECT dateColumn FROM table WHERE numberColumn = 3")
return selectResult
if __name__ == "__main__":
createTables()
and here is my app.py code;
import web
import SnakeSQL
import createdb
render = web.template.render('templates/')
connection = SnakeSQL.connect(database='test')
cursor = connection.cursor()
urls = (
'/', 'index'
)
class index:
def GET(self):
createdb.createTables()
result = createdb.select()
return render.index(result)
if __name__ == "__main__":
app = web.application(urls, globals())
app.run()
I couldn't find out why I am having this error. Can you please share your knowledge for solving this problem?

Answer 1

First off, the SnakeSQL docs appear to be from 2004, the actual code was last updated in 2009, and the author states that the project is no longer maintained. You may want to consider using something still actively maintained instead.
The docs also mention:
In theory, one of the processes accessing the database could get stuck in an infinite loop and not release the lock on the database to allow other users to access it. After a period of 2 seconds, if the process with the current lock on the database doesn't access it, the lock will be released and another process can obtain a lock. The first process will itself have to wait to obtain a lock.
Looking at your traceback, I'll make an educated guess that since you put the cursor at module level (which again, you probably don't want to do), it created the cursor when the module was first imported, then by the time your program actually ran the createTables function, more than 2 seconds had elapsed, and it has given up the lock.
Try moving the line to create your cursor inside your methods:
def createTables():
cursor = connection.cursor()
cursor.execute("CREATE TABLE table (dateColumn Date, numberColumn Integer)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2003-11-8', 3)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2004-11-8', 4)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2005-11-8', 5)")
cursor.execute("INSERT INTO table (dateColumn, numberColumn) VALUES ('2006-11-8', 6)")
def select():
cursor = connection.cursor()
selectResult = cursor.execute("SELECT dateColumn FROM table WHERE numberColumn = 3")
return selectResult
(and do the same in your app.py code).